1. Field of the Invention
This invention relates to a signal processor and a tracking method of signal search range to process an externally input signal.
2. Related Art
The signal processor is provided with various functions (for example, see Japanese Unexamined Patent Application Publication No. Hei 2-21266). The invention of the publication is a signal processor (revolution indicator) to measure the number of revolutions of a revolving motor, which detects a leakage flux as a phenomenon resulted by the revolution of a rotor, finds the spectrum data of the leakage flux by fast Fourier transformation, and finds the number of revolutions of the revolving motor based on the frequency showing the maximum value of the spectrum data.
However, the spectrum data FFT-computed by such a revolution indicator contains not only the main component spectrum (first order component), which becomes the number of revolutions of the revolving motor, but also many spectrums such as half order, second order, and third order. Generally, the spectrum showing the maximum value in the spectrum data becomes the main component of the revolution to be computed, but due to the influence by disturbances, etc. to the revolving motor, or depending on the kind of signals measured as a phenomenon resulting from the revolution used for the measurement, there has been a problem in that the above described spectrums such as half order, second order, and third order spectra becoming larger than the spectrum of the main component causing an incorrect read out that is a different spectrum as the main component spectrum.
Hence, a measure has been taken so that the search range to search the main component spectrum is set to exclude the above described frequency components such as half order, second order, and third order. For example, the lower limit of the search range is set to 0.6 times of the main component and the upper limit is set to 1.8 times of the main component, and on the frequency axis, the spectrums of half order and second order adjacent to the main spectrum (first order component) are excluded. However, with such a setting of the search range, when the number of revolutions of a revolving motor is varied, the spectrums such as half order, and second order other than the main component are included within the search rang to cause the wrong read out of those spectrum as the spectrums of the main component resulted resulting from the number of revolutions of the revolving motor.
To be more precise, when the main component of the revolving motor is 100 Hz and the search range of the main component is set to 60-180 Hz, 50 Hz of the half order component and 200 Hz of second order component are excluded from the search range. However, when the main component of the revolving motor varies from 100 Hz to 150 Hz, within the search range (60-180 HZ), 75 Hz, which is the half order component of the varied main component (150 Hz) is read out, and in the case that the spectrum of the main component (150 Hz) is smaller than that of the half order component (75 Hz), the spectrum of the half order has sometimes ended up to be read out as the main component. Moreover, there has been a problem in that, also when the main component deviated from the search range (60-180 Hz) (for example, 200 Hz), spectra such as half order other than the main component has ended up to be read out.